Diamond abrasive wheel



PmmedMsyzim Lowell H. hlllligan, Worcester, Mala, assignor to Norton Company, Worcester, Mass., 2. corporation Massachusetts No man. Application Serial No. as,"

8 claims. (CL 51-408) The invention relatesvto diamond abrasives.

One object of the invention'is to provide a composition for the manufacture of vitrified diamond grinding wheels 1 which will permit the wheel to be manufactured by means'oi relatively simple apparatus. Another object of the invention is to rovide a low fusing point bond for the manufacture of diamond grinding wheels in order that the wheels may be fired in an air atmospher thus getting rid of complicated furnaces and gas tanks,'piping' and the like. Another object of the invention is-to provide a ceramic compositionof such characteristics that 7 diamond grinding wheels can be made therewith in a small shop without the use of elaborate fur-.

nace equipment. Another object is to provide a vitrified diamond grinding wheel of free cutting characteristics. Another object isi'o provide a vitrified" diamond grinding wheel of good all around characteristics for the .grindingof hard materials. V 1

Other objects will be in'part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements and arrangements of parts all as will be illustratively described herein and the scope of the application of which 'will be indicated in the following claims. I Vitrifled diamond grinding wheels have found a definite place in industry and for some pur-.

poses are preferred to any other kind of grinding wheel including resinoid bonded diamond wheels and metal bonded diamond wheels. The manufacture of vitrified bonded diamond wheels has however been expensive because the vitrifying process required temperatures higher than any required to cure aresinoid and higher than required to sinter metal powders. Furthermore in order to protect the diamonds against oxidation, non-oxidizing gases have usually been introduced into the furnace and this is to say the least has been a nuisance.

In the manufacture of ceramic bonded grind- TABLEI Wheel formulae Volume Percentages No. 1 No. 2 No. 3 No. 4

R c R c R c R 0 Diamond 17.8..... 17.8..... 17.8..... 11.3..... VitreousSilica.. 13.8..... 11.5. 10.0.-. 16.0 mm Refractory Glass. 11.2 21.2 12.2 18.5 17.2 10.0 11.2 10.0 rm. 50.0 50.0 58.0 58.0 50.0 50.0 50.0 50.0 Pores 15.0 15.0 12.0 12.0 15.0 15.0 1.5.0 m0 Total o|100. 0 100. 0|10o. olloo. 01100. 0|100. 0|100. 0

2 ing wheels generallyfdmat treatment has cuttomarily involved the attainment of tempera-. tures of the order of 1200 C. Special ceramic bonds for diamond grinding wheels which mature at temperatures of aroundiOili) C. have been developed and they avoid graphitization of the small diamond fragments. I have now dis-' covered a ceramic bond which satisfactorily holds the diamond fragments and which can be matured at temperatures below 750 C. and yet makes a vitrified diamond grinding wheel which is equal to or superior to previous vitrified diamond wheels in many grinding operations. With the use of this bondand this low vitrifying temperature, graphitization of the diamonds cannot occur and no precautions need be taken to prevent oxidation of the diamonEand thus a simple inexpensive furnace can be used.

I have manufactured four vitrified bonded diamond grinding wheels in accordance with this invention, each wheel having a non grinding center and a' diamond containing rim. Each wheel was molded 6" in diameter by V thick and had a 1 /4" central hole and the abrasive rims had a radial depth of M; of an inch. These were all straight" wheels, that is to say they all had the shape of a disc. The compositions of Essie wheels ar fully disclosed in the following es: s

- Ilring Temp. for one hour soak (3-- In Table I the letter R. stands for rim and the letter C stands for center. In this table the inert refractory glass was crushed glass of such a high fusing point that it was not importantly softened during the maturing of the bond which of course is the frit. This inert refractory glass had the composition shown in Table III.

TABLE III Inert refractory glass The inert refractory glass of Table III does not soften sufilciently for bonding at 750 C. and constitutes a filler in the wheel rim and center. The vitreous silica likewise does not soften at 750 C. and constitutes a filler in the wheel center. Diamond of course is the abrasive and is the material that is to be bonded by the ceramic bond. The frit therefore constitutes the effective bond, that is to say it is the only ingredient which is softened for bonding during the firing. The pores of course represent space.

The frits are glasses having the formulae given and were made by mixing together ingredients to produce compositions having such formulae, then fusing together the ingredients to produce a read y pourable liquid, then pouring this liquid into water which congealed the composition and created many cracks due to thermal shock, then milling the resultant glass to a fine powder. The frit identified by the numeral 1 in Table II was the frit used in wheel No. 1 and so on.

It will readily be noted that the frit formulae are low in silica which is usually the predominating oxide in a glass and which is refractory. The zinc oxide and the lead oxide or the combination of the two in combination with the boric oxide forms a strong glass that well bonds the diamonds and which has a softening point under 750 C. In this connection softening is defined as softening sufiiciently for good bonding.

The bond of the invention can be defined as a bond comprising boric oxide in an amount of 35% to 60% and heavy metal oxide in an amount of about 20% to 65% and selected from the group consisting of the oxides of zinc and lead and mixtures thereof. said bond having a softening point for good bonding under 750 C. In one species of the invention the bond comprises boric oxide 35% to 60% and zinc oxide 40% to 65% having a softening point for good bonding under 750 C. and in another species the bond comprises boric oxide 35% to 60% andlead oxide 20% to having asoftening point for good bondingunder'lbOC. Inallcasesthebondisa prefitted bond, that is has been completely fused to a clear glass then solidified and crushed. all before the mixing with abrasive, etc. In all cases the silica content should be kept low in the int, that is not exceeding 10%. According to the main features of this invention these are the bonds used to bond the diamonds. Preferably also these bonds are used for the center of the wheel.

A diamond grinding wheel made in accordance with this invention as above defined will grind eflectively and will have the great advantage that it can be made at less cost because the bond matures at a low temperature.

Wheels 1, 2, 3 and 4 were tested for grindin performance against standard vitrified bonded diamond wheels which were considered to be the best vitrified bonded diamond wheels on the market. In these tests a surface grinder was used which rotated all the wheels at 5500 surface feet per minute speed, giving mills of cross feed per traverse stroke. and one mill of down feed per complete cross feed. Ineach test the conditions were the same for each individual grinding operation. The dimensions of the wheels according to the invention have already been given and the dimensions of the standard wheels were the same. The general conditions for each test are above given and all other conditions were maintained the same as nearly as possible. The results of the tests are shown in Tables IV, V and VI. In the tests of all these tables the general conditions were the same and are as above given. Specific conditions differed between the tests of the diflerent tables but were the same for all the testing reported in a given table. In the tests of Table IV the table traverse was 440 inches per minute and the total down feed was 20mins. In the tests of Table IV the work piece was two areas one inch by five inches of cemented tungsten carbide (including some other carbides) on either side of an area one-half inch by five inches of soft steel, thus being a composite work piece two and one-half inches by five inches.

In the tests of Table V the table traverse was 400 inches per minute and the total down feed was mills. In the tests of Table V the work piece area was five inches by five inches and the work piece was cemented tungsten, tantalum, columbium and titanium carbides of a different grade from that of Table IV. In the tests of Table VI the conditions were the same as for the tests of Table V except that the area of the work piece was two and one-half inches by six inches, the work piece being of the same material as in the tests of Table V.

In each case two test runs were made with each wheel and the tables show results of each test run and then give the average of the two runs.

'emciency of a wheel ram-s v Wheel Wear Materia 1 Index of Net Wm on Diameter Removed I Power Mill: Mall Watt: 2 2. 4 28. 5 796 2.0 28.9 7%

Average 2. 2 28. 7 100 Average 6.9 26. 244

a 18. 4 2o. 7 212 m. 4 19. 6 181 Average l9. 4 a). 2 196 Average 2 28. 7 736 TABLE VI Wheel Wear Material Index of Net wheel Number on Diameter Removed 'Power mu; Muu Wear 3 17. 8 21. 2 147 17. 5 21. 3 152 Average l7. 7 21. 3 150 Average 7. 6 24. 0 232 Average. 19. 6 20. 8 211 b i. 13. 7 22. 9 256 12. 1 2a. 4 204 Average l2. 9 23. 2 230 Average 7. 5 26. 0 r 288 The standard wheel used as a comparison for the tests of Table IV is identified by theletter b, the standard wheels used for comparison for the tests of Table V are identified by the letters a. and it while the standard wheels used for comparison for the tests of Table VI are identified by the letters a, b, and c. All of these standard wheels had 25 volume percent diamonds in the abrasive part. In such abrasive part, wheel a had 30 volume percent pores, wheel 5 had 25 volume percent pores, wheel 0 had volume percent pores and wheel it had 15 volume percent pores. In such a series of wheels the harder acting wheels are those having the lesser volume percentage of pores.

In comparing the results given in the tables it is to be noted that other factors being equal, the more material a wheel removes the better is the wheel, other factors being equal the less the wheel wears the better is the wheel. WhlIe the shown by material removed divided by wheel w ar, there are other factors to be taken into account in a grinding operation.

For example in the case of two wheels whose efflciency ratio is the same, the one which removes the most material in a given operation may be preferred for the reason that the labor cost will be lower. The table showing the net power in watts is significant insomuch as the less power used the better is the wheel, other conditions being the same because lower power. indicates free cutting. In the tests reported in these tables grinding pressure is not indicated so the figures on material removed and wheel wear do not in themselves tell the complete story butby recording the net power in watts, there is given complete information for appraising the wheels.

Referring now to Table IV, wheel No. 1 according tothe invention is clearly superior for that grinding operation to the standard wheel b.

Wheel No. 1 showed a wheel wear only a little overhalf that of wheel I) while wheel No-1 re- I moved more material than wheel b. Wheel b was evidently slightly freer cutting than wheel 1 but the difference is too small to overcome the other indications that wheel 1 is superior to wheel I) in that type of grinding. I g

Considering now the results shown in Table V, wheel No. 2 according to the invention is clearly a good wheel. While it shows slightly more power used than wheel :1, it shows slightly less wheel wear and the material removed is the same for wheels 2 and d. Wheel No. 2 is very much superior to wheel a with regard to wheel wear so much so that this superiority is not offset by the greater amount of power used in the case of wheel 2. Wheel 4 shows low power and while wheel a shows slightly lower power, wheel a wore very much more than wheel 4. These wheels 2 and 4 are therefore in some respects superior to standard wheels and since they can be manufactured much more easily than standardwheels, wheels 2 and 4 show an overall superiority considered from all points of view.

Considering now Table VI, wheel 4 shows less wheel wear than wheels 0 and b and about the same as wheel 0. Wheel 4 shows about the same material removed as wheels a, b and c and also is in the same range so far as power consumption is concerned. Again the relative ease of manufacturing wheel 4 makes it an overall superior wheel. Wheel 3 shows a lower consumption of power offsetting the greater wheel wear as compared to wheel c for example.

There are many operations where a free cuttingwheel is demanded regardless of the efllciency factors and for such operations wheels such as wheel 3 will be preferred.

Summing up the tests as shown in the tables, wheels according to this invention are quite competitive with standard wheels for grinding cemented carbides and since they are more easily manufactured an overall improvement is shown.

It will thus be seen that there has been provided by this invention a ceramic composition for the manufacture of diamond abrasive wheels in which the various objects hereinabove set forth together with many thoroughly practical ad.-

selected from the group consisting of the oxides.

of zinc and lead and mixtures thereof, said bond having a softening point for good bonding under 750 C. and said bond having a silica content below 10%.

2. An abrasive wheel comprising diamonds united by a prefrltted bond comprising boric.

in an amount of 20% to 45%, said bond haviizig a softening point for good bonding under 750 C., and said bond having a silica content below 10%.

LOWELL H. MJLLIGAN.

- REFERENCES CREE) The following references are .of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 104,231 Van Kleeck June 14, 1870 155,461 Ott Sept. 29, 1874 Number 5 Number Name Date Caesar Apr. 2, 1878 Thomas Apr 27, 1920 Locke et al Mar. 10, 1925 Taylor Oct. 29, 1935 Taylor Oct. 29, 1935 Vuilleumier Sept. 26, 1939 Martin Jan. 7, 1941 Tillyer et al Sept. 2, 1941 Houchins Oct. 21, 1941 Houchins Nov. 16, 1943 Ba'stick et al Aug. 27, 1946 FOREIGN PATENTS Country Date Great Britain Jan. 3, 1939 Great Britain Jan. 8, 1941 Italy Nov. 24, 1928 The Netherlands Feb. 16, 1942 

1. AN ABRASIVE WHEEL COMPRISING DIAMONDS UNITED BY A PREFRITTED BOND COMPRISING BORIC OXIDE IN AN AMOUNT OF 35% TO 60% AND HEAVY METAL OXIDE IN AN AMOUNT OF 20% TO 65% AND SELECTED FROM THE GROUP CONSISTING OF THE OXIDES OF ZINC AND LEAD AND MIXTURES THEREOF, SAID BOND HAVING A SOFTENING POINT FOR GOOD BONDING UNDER 750*C. AND SAID BOND HAVING A SILICA CONTENT BELOW 10%. 